Incrementally controllable-thrust propulsion device



July 29, 1969 I J. TROTEL 3,457,726 1 INCREMENTALLY CONTROLLABLE-THRUSTPROPULSION DEVICE I Filed July 24, 1967 4 Sheets-Sheet 1 Z Jicques790751,

Avnw we i 29, 1959 I J. TROTEL 3,457,726

INCREMENTALLY CONTROLLABLE-THRUST PROPULSION DEVICE Filed July 24, 19674 Sheets-Sheet 2 July 29, 1969 J. TROTEL 3,457,726

INCREMENTALLY CONTROLLABLE-THRUST PROPULSION DEVICE Filed July 24, 19674 Sheets-Sheet s July 29, 1969. 4. wow... 3,457,726

INCREMENTALLY CONTROLLABLE-THRUST PROPULSION DEVICE Filed July 24, 19674 Sheets-Sheet I.

United States Patent Int. Cl. rozk 9/04, 9/06 US. Cl. 60-250 19 ClaimsABSTRACT OF THE DISCLOSURE The controllable-thrust motor for manoeuvringof spacecraft and the like comprises a sealed capsule (1) having a jetdischarge orifice (13) at its rear end and containing a composite chargeconsisting of alternating layers of fuel, e.g. ammonium perchlorate (4)and inert material e.g. aluminium foil (5). A heating electrode (6) isspring-pressed against the outermost layer so that the application of acurrent pulse from an electric source (B) through discharge of condenserC will vaporize the outermost inert layer (5A) and burn only theadjacent fuel layer (4A), generating a predetermined increment ofthrust. Reference is had to FIG. 1.

This US. application is based under International Convention on Frenchpatent application 70,865 filed July 26, 1966 by the assignees.

Reference is made in the disclosure to co-assigned, U.S. Patent No.3,398,357.

This invention relates to propulsion devices or motors capable ofdeveloping a controllable thrust, of the kind used as auxiliary motorson space vehicles for such purposes as modifying the attitude of thevehicle, controlling its orbit, and similar maneuvering and correctingfunctions.

Conventional devices of this kind have often used a stored pressure gas,such as nitrogen, to produce a controllable propulsion jet. Such devicesare simple and convenient to control, but the need to carry a heavy andbulky pressure vessel to store the gas is a serious hindrance.

In co-assigned, US. Patent No. 3,398,537, there is disclosed a novelform of controllable thrust propulsion device or auxiliary motor, whichcomprises a charge of solid fuel enclosed in a sealed casing having anoutlet orifice for the discharge of a gaseous reaction jet. The fuelcharge has a composition so predetermined as to undergo a controllablechemical reaction preferably of a mildly exothermic character onapplication of heat energy thereto, and a controllable of heat isassociated with the charge capable of controlling the progress of thereaction and thereby controlling the thrust developed by the device.

The device just referred to is simple, compact, light and efficient.However, further experimentation therewith has shown that in somecircumstances the thrust derived therefrom is difiicult to control asaccurately as would be desirable, because the rate of combustion of thecharge tends to be unstable, especially depending on the cold or hotcondition of the motor and the surrounding temperature, and also on theamount of the remaining charge.

It is an object of the present invention to provide acontrollable-thrust propulsion device using a solid fuel charge andhaving the outstanding advantages of the device disclosed in theco-pending application, and in which moreover the charge combustion hasvery high stability,

3,457,726 Patented July 29, 1969 making possible precise incrementalcontrol over the developed thrust. An object is to provide such a devicewhich can be accurately controlled incrementally as to the timing andamount of the thrust developed thereby, through remote control meanssuch as by digital signals or pulses received from a remote controlstation or automatic control means. An object is to provide a simple,compact, lightweight, reliable, solid-charge, incrementallycontrollablethrust propulsion device especially suitable for use as an auxiliarymotor on board space vehicles, which can be operated intermittently orcontinuously with a high degree of precision.

The device of the invention is characterized in that it uses a compositesolid fuel charge consisting of alternate layers of fuel and separatormaterial. Heating means, such as an electrode, when energized firstevaporates the outermost layer of inert material or separator, and willonly then ignite the next adjacent fuel layer, combustion of which thenproduces the useful increment of thrust. The separator layers are sopredetermined that the combustion of a fuel layer cannot vaporize thenext adjacent separator layers, so that combustion is arrested, and withit the developed thrust, on complete combustion of each layer. In thisway, the device can be operated for accurately predetermined periods oftime.

FIGS. 1 to 5 are views in axial section illustrating five differentforms of embodiment of the device of this invention.

In the first embodiment, shown in FIG. 1, the device comprises a metalcontainer 1 of generally cylindrical form having one end sealed by afiat end wall 2 and its other end 12 domed and formed with a centralorifice 13 for discharge of the propulsion jet. A flared nozzle 14 isshown as extending around and rearward from the jet orifice 13. Thecasing or container 1 may be made of any suitable strong material, suchas stainless steel.

Within the casing 2 is a composite fuel charge which as shown consistsof a stack of combustible fuel layers 4 and inert separator layers 5 inalternation. The fuel stack has one end adjacent the end wall 2 and itsother end somewhat short of the domed end section 12 of the casing. Theoutermost end of the stack is formed by an inert separator layer 5A, andthe next adjacent fuel layer immediately below it is designated A4.

The inert separator layers 5 ma comprise thin metal foil, e.g. aluminiumfoil about 0.05 mm. thick, or they may comprise other suitable materialsas later described.

The heating means in this embodiment comprises a conductive electroderod 6 extending into the casing 1 through the jet discharge nozzle andorifice, and supported in axially centered position through suitablemeans shown as including a bushing 7 of heat resistant materialsupported by way of an insulating spider support 14 at the outer end ofthe nozzle 21. Bushing 7 is extended rearward in the form of aprotective sheath 71 surrounding rod 6. Electrode rod 6 is freelyslidable in bushing 7 and is pressed at all times into tight contactengagement with the outermost separator layer 5A of the fuel-chargestack by means of a tension coil spring 8 surrounding the rod and havingits outer end anchored to the outer end of the rod, while the inner endof spring 8 is anchored to bushing 7. Clearly various other springbiassing arrangements may be used for the purpose of pressing rod 6against the fuel stack.

A heating circuit is shown as including a voltage source E, which may beany suitable source available aboard the spacecraft, e.g. a solarbattery. A capacitor C is connected to source E in series with aresistance R, and one side of capacitor C is connected to the outer wallof easing 1, while the opposite end is connected through a cut-offswitch S and a flexible or otherwise deformable connection to the outerend of electrode rod 6.

In operation, capacitor c is at all times charged from the source Ethrough protective resistance R. On closure of switch S, the capacitordischarges through the circuit including rod 6, the outermost layer ofmetal foil 5A in the stacked charge, and the wall of casing 1. The highvoltage discharge from the capacitor C instantly vaporizes the foil 5A,and almost simultaneously ignites the now exposed, underlying fuel layer4A. Combustion of the fuel produces a large volume of combustion gaseswhich issue out of orifice 13 and through nozzle 21, as a high-velocityjet generating the requisite thrust. The time required for completecombustion of a fuel layer of course depends on the thickness of thelayer and the nature of the fuel, and can be varied widely by suitablyselecting said thickness. The inert separator elements 5 are sopredetermined that the heat generated by the combustion of the adjacentfuel layer is incapable of vaporizing the separator element, nor is saidheat capable of igniting the next fuel layer sealed off by theseparator. Practical experience has shown that these conditions can bereadily achieved while still providing separator elements thin enough toensure their being completely and practically instantaneously vaporizedby the electric discharge passed therethrough as described above.

Thus the combustion and therefore also the thrust from the device isarrested on combustion of each fuel layer. If switch S is again actuatedto its closed condition immediately on termination of the combustion ofthe layer, the above described process is repeated immediately, andthere need be virtually no interruption in the thrust developed by thedevice. If desired however, and this is an outstanding advantage of thedevice disclosed, the switch S can be retained in its open-circuitcondition for any desired period of time, so that impulses of thrust ofany desired incrementally controllable duration can be generated atprecisely controlled times.

As will be understood, the electrode 6 projects further and further intothe casing 1 under the action of spring 8, as the fuel charge is usedup.

The solid fuel used in the laminated or stacked charge of the inventionmay include any of the compositions known as suitable for use as a solidfuel. Examples of suitable fuel compositions include the following(compositions are by weight):

Ammonium perchlorate (80%) and asphalt (20%);

Ammonium perchlorate (75%) and polyurethane (25% Ammonium nitrate (76%)and cellulose acetate (14%);

Nitrocellulose (55%), nitroglycerine (25%) and plasticizer.

The above list is not exhaustive but merely indicative. The compositionsalso are only indicative and may generally be varied over a substantialrange without impairing results.

As the inert constituent in the separator layers, it will be understoodthat in the embodiment of FIG. 1 this must be an electrically conductivematerial in order to establish a conductive path through the dischargecircuit for capacitor C. Conveniently, the separator layers in suchcases may comprise aluminium foil about from to A mm. thick, throughother suitable conductive media may be used.

FIG. 2 illustrates a modification of the controllablethrust motor ofFIG. 1 in which similar components are designated by similar numerals.The only important difference here is that the metal container 2 isprovided with an end sealing wall 2 which, rather than being flat as inFIG. 1, is conically convex with a rounded central apex.correspondingly, both the combustible fuel layers 4 and the interveninginert separator layers 5 are of a similar generally conical concaveconfiguration as the end wall 2. An advantage of this arrangement isthat the combustion area of each fuel layer is substantially greater,for a given volume, than in the case of FIG. 1. Moreover the recessedcharge configuration obtained with such an arrangement creates aconcentration of heat tending to improve combustion.

In the further embodiment shown in FIG. 3 the controllable-thrust devicecomprises a generally cylindrical container 1 made of a suitableferromagnetic material, e.g. suitable grade of magnetic steel, and thereis provided a rod or post 9 of the same material extending from the flatend wall 2 of the container axially thereof. The free end of axial post9 lies substantially flush with the rear wall 25 of casing 1 and definesan annular gap 22 with a central aperture in said front wall for thedischarge of combustion gases. The annular gap 22 is surrounding by asuitable converging-diverging wall defining the jet nozzle orifice 13.Positioned within the front end of easing 1 near the end wall 2 thereofis a coil winding 10 surrounding post 9. The coil 10 has its ends ledout of easing 1 and connected to a condenser discharge circuit similarto the one described for FIGS. 1 and 2. Overlying coil 10 in thecontainer is a separator disc 23 of non-magnetic material. The remainingpart of the container 1 to the rear of disc 23 and extending over themajor part of the axial length of the device is an assembly of coaxialcylindrical lamina tions including active fuel layers 4 and electricallyconductive separator layers 5 in alternation. The radially innermostseparator layer 5 is radially spaced from the circumference of post 9 toprovide an annular cylindrical gap in which initial combustion can takeplace. In the operation of this device, it will be understood that coil10 constitutes the primary of a transformer of which each of theconductive separator layers 5, made e.g. of aluminum foil as in thepreceding embodiments, constitutes a partial secondary. On closure ofswitch S, the COndenser C discharges into coil 10, creating a highprimary current pulse through the coil winding. It will be evident thatthe impedance of the secondary circuits constituted by the metal foillayers 5 increases stepwise from each such layer to the next radiallyoutward layer owing to the increase in radius, hence, every time switchS is closed the primary current pulse generated in coil 10 induces asecondary current pulse predominantly or exclusively in the innermostseparator foil 5 present at the time. The high current pulse produces asudden and sharp discharge of heat which vaporizes the foil, exposingthe adjacent fuel layer for combustion as earlier described. Thisembodiment is considered advantageous in that it eliminates theprovision of a movable heating electrode in the path of the gas jet, asrequired in FIGS. 1 and 2.

In the embodiment of BIG. 4, the general lay-out of container 1 with itsactive and inert stacked layers 4 and 5 is similar to that in FIG. 1.However, the heating means used in this case comprise a resistive wire11 disposed e.g. in the form of a flat grid in container 1 some distancefrom the rearmost inert layer 5A. The ends of resistor 11 are connectedto rigid conductors 15 and 16 which serve as supports therefor and areled out of container 1 for connection to a pulse circuit which may besimilar to the condenser discharge circuit shown in the precedingembodiments. A reflective screen 17 made of a suitable metal sheetelement having a polished rear surface, is supported a short distancerearward of register grid 11, e.g. from the rigid resistance-support ingwires or other suitable supporting means not shown. Reflector 17 isshown flat but may be concave if desired. On application of a currentpulse to resistor 11, the resulting heat is reflected by screen 17 as abeam of heat radiation which evaporates the nearest inert layer 5,exposing the underlying fuel layer 4 for combustion as earlierdescribed.

The embodiment shown in FIG. 5 is somewhat similar in its method ofheating as the one just described, but the general layout resembles thatof FIG. 3 rather than FIG. 1. That is, the active and inert layers 4 and5 are in the form of coaxial internested cylindrical layers coaxial withthe cylindrical casing 1 and defining a central recess Within thecasing. A heating resistor ,11 in the form of a helical wire issupported in this central recess by way of the condutcors 15 and 16connected to a pulsing circuit not shown. On application of a currentpulse to the resistor 11, the heat radiated outward from the resistorevaporates the innermost separator layer and causes combustion of thefuel layer 4 thus exposed.

In each of the embodiments of FIGS. 4 and 5 the active fuel constituentmay be similar to any of those used in the embodiments of FIGS. 1 to 3.On the other hand, the separator constituent in each of said embodimentslast described is not necessarily electrically conductive, but maycomprise any of various suitable noncombustible materials capable ofbeing decomposed and/ or evaporated or sublimated by heat. It is alsocontemplated, in embodiments of the invention of the'character lastdescribed, that the constituent comprising the inert or separator layers5 may be such as to generate a substantial amount of gas capable ofcontributing to the thrust developed by the device, as said constituentis decomposed by heat. Strictly speaking in such embodiments thematerials composing the separator layers are not inert but, to someextent, active. In fact said separator layers may comprise materialssimilar in char acter to some of those used as the fuel material in theco-pending application Ser. No. 553,814 referred to above.

As examples of materials usable as the relatively inert separatormaterials in embodiments of the present invention of the typeexemplified by FIGS. 4 and 5 the following may be cited: Organicpolymers such as polyvinyl chloride, polystyrene and the like; celluloseacetate; urea-formol resins, methacrylates, polyesters, polysulfides,polyurethanes, polybutadiene.

FIGS. 4 and 5 are but examples of embodiments of the present inventionin which the source of heat serving to break down the separator layerand ignite the exposed combustible layer, is other than an electricdischarge. Various other heat sources of this general character may beconceived for use according to the invention, including the sourcesdisclosed in the above-identified co-pending application, e.g. sunlightor, a source of radioactive substance. Thus, the co-pending applicationdiscloses arrangements wherein the casing of the device includes atransparent wall section arranged to be exposed to sunlight by means ofa movable opaque shutter, for igniting the charge. In anotherarrangement disclosed in said copending application, the heat source isan element of radioactive material movable into and out of the casing ofthe device for controlling charge ignition. Controllable heat sources ofeither of these types can be used in devices according to the presentinvention for breaking down the separator layers and igniting theexposed fuel charges of the various devices disclosed herein.

Conveniently, though not necessarily, the individual layers of fuelmaterial in a device according to the invention are so predeterminedthat the combustion of each layer develops substantially the same thrustincrement. Where necessary, as in the embodiments of FIGS. 3 and 5, thiscondition may require the provision of unequal thicknesses for thevarious fuel layers. With such an arrangement, the average thrustdeveloped will be constant when the rate of ignition of the charges willbe constant. When it is desired to vary the average thrust developed bythe device, the rate at which the successive fractional charges areignited, e.g. the rate at which such as S in FIGS. 1-3 is closed, wouldbe varied correspondingly. Control is thus facilitated. As regards thesensitivity with which the developed thrust can be controlled and variedwith the controllable-thrust motors of the invention, this willobviously be increasingly great as the number of elementary fuel chargesin the device is large, and the individual quantity of fuel in eachelementary charge is correspondingly small.

The means for controlling the ignition of each individual fuel charge,shown as a mechanical switch S in the embodiments of R168. 1-3, mayassume a variety of forms, and may be associated with any suitableautomatic and/or remote-control instrumentalities, e.g. for operatingthe control by way of a radio link or under control of gyroscopic andinertial stabilizing arrangements, as will be readily understood.

What I claim is:

1. An incrementally-controllable thrust device com prising:

a casing (1) having an outlet orifice (13) for the discharge of agaseous jet;

a composite laminated charge in said casing comprising a series ofcombustible fuel layers (4) and a series of separator layers (5) inalternating relation; and

a single ignition means (S, 6; S, 10; 15, 16, 11) for applying pulses ofthermal energy to said charge, each of said energy pulses provided bysaid single ignition control means causing combustion of a single one ofsaid fuel layers (4) to develop a corresponding increment of thrust fromthe device.

2. The device claimed in claim 1, wherein said charge comprises a stackof fiat fuel and flat separator layers.

3. The device claimed in claim 1, wherein said charge comprises a stackof internested concave fuel and separator layers.

4. The device claimed in claim 1, wherein said charge comprises a set ofinternested coaxial cylindrical fuel and separator layers.

5. The device claimed in claim 1, wherein said single ignition controlmeans comprises a source (E) of electric energy, capacitance means (C)connected to be charged from said source, and discharge circuit means(S, 6, 5A, 2; S, 10; 15, 11, 16) connected for receiving dischargepulses from said capacitance means for producing said pulses of thermalenergy.

6. The device claimed in claim 5, wherein said casing (1) and saidseparator layers (5) are electrically conductive and said dischargecircuit means includes: a conductor member (6) engageable with anexposed one (5A) of said conductive separator layers and establishing acircuit extending through said exposed layer and said casing; and meansconnecting said conductor member and said casing to said capacitancemeans (C).

7. The device claimed in claim 6, including spring means (8) associatedwith said conductor member (6) for pressing it into resilient engagementwith said exposed separator layer (5A).

8. The device claimed in claim 5, wherein said casing has magnetic coremeans (1,9) associated therewith and said separator layers (5) areelectrically conductive, and said discharge circuit means includes aninductance coil (10) associated with said casing to constitute theprimary winding of a transformer having secondaries constituted by saidseparator layers (5), said separator layers (5) being so disposed insaid laminated charge that the impedance of each separator layer isgreater than the impedance of the adjacent separator layer that hasundergone combustion before it.

9. The device claimed in claim 8, wherein said charge comprises a set ofinternested coaxial cylindrical fuel and separator layers, and saidmagnetic core means includes a rod (9) extending axially with respect tothe cylindrical set.

10. The device claimed in claim 1, wherein said ignition control meanscomprises a source of electric energy and a resistance (11) connected tosaid source and arranged to radiate heat on an exposed one (5A) of saidseparator layers.

11. The device claimed in claim 1, wherein said fuel comprises a solidrocket propellent composition.

12. The device claimed in claim 1, wherein said fuel comprises acompound of ammonium perchlorate and asphalt.

13. The device claimed in claim 1, wherein said fuel comprises acompound of ammonium nitrate and cellulose acetate.

14. The device claimed in claim 1, wherein said fuel comprises acompound of ammonium perchlorate and polyurethane.

15. The device claimed in claim 1, wherein said fuel comprises acompound of nitrocellulose, nitroglycerine and plasticizer.

16. The device claimed in claim 1, wherein said separator comprises thinmetal foil.

17. The device claimed in claim 1, wherein said separator comprisescellulose acetate.

18. The device claimed in claim 1, wherein said separator comprisesorganic polymer material.

19. The device claimed in claim 1 wherein said outlet orifice issubstantially centrally located at one end of said casing and whereinsaid composite laminated charge comprises a stack of alternate generallytransversal solid propellent layers and conductive separator layers, theedges of said separator layers engaging the inner surface of saidcasing, and wherein said single ignition control means comprises:

a conductor members passing through said orifice and engageable with anexposed surface of one of said separators;

a source of pulses of electrical energy; and

terminal means on said conductor member and on said casing coupled tosaid pulse source;

each pulse delivered by said pulse source vaporizing one separator layerand causing combustion of a single one of said propellent layers todevelop a corresponding increment of thrust from said device.

References Cited UNITED STATES PATENTS 2,640,417 6/1953 Bjork et al.60-2-56 2,918,871 12/1959 Taylor l0246 XR 3,000,175 9/1961 Lawrence149-76 XR 3,002,830 10/1961 Barr 149-76 XR 3,033,716 5/1962 Preckel149-96 3,128,600 4/1964 Oldham 6025O 3,247,796 4/1966 Kirshner l02463,248,875 5/1966 WOlcott 60250 XR 3,249,049 5/1966 Zimmerman l02463,293,855 12/1966 Cuttill et a1 602 56 XR 3,358,452 12/1967 Ehrenfeld etal. 60-200 FOREIGN PATENTS 137,341 9/1952 Sweden. 627,722 8/ 1949 GreatBritain.

25 CARLTON R. CROYLE, Primary Examiner US. Cl. X.R.

